The present invention relates to methods for controlling a hybrid compressor system having a refrigerant compressor that is selectively driven by an engine or an electric motor, and to methods that optimize the electric motor""s operation and efficiency.
Conventional automotive air conditioning systems generally include a refrigeration circuit having a refrigerant compressor. Typically, the compressor is driven by the engine via a drive belt. As the compressor is driven by the engine, the refrigerant circulates in the refrigeration circuit absorbing heat from the passenger compartment thereby providing a cooling effect. The compressor is typically coupled to the vehicle""s engine via an electromagnetic clutch. Thus, when the cooling capacity of the refrigerant circuit outweighs the thermal load on the circuit, the electromagnetic clutch disengages the engine thereby halting the operation of the compressor. Furthermore, conventional automotive air conditioning systems do not operate when the engine is off, thus the passenger compartment may not be cooled when the engine is off.
However, an automotive hybrid air conditioning system known in the art to include a xe2x80x9chybrid compressorxe2x80x9d are selectively driven by an engine or an electric motor. These hybrid air conditioning systems may be driven by the engine while the engine is running and by the electric motor when the engine is not running to effect cooling on the passenger compartment. Typically, a hybrid compressor is a refrigerant compressor having a driveshaft, wherein an electric motor is coupled to the driveshaft and an electromagnetic clutch is connected to an output shaft of the output motor. Typically the engine is connected to the output shaft through the clutch. When the clutch is turned on, engine power is transmitted to the driveshaft through the output shaft, which operates the compressor. The output shaft of the motor rotates with the driveshaft of the compressor. The rotation of the output shaft generates electromotive force in the motor. This electromotive force may be used to charge the battery. However, when the engine is turned off, the clutch is turned off and the output shaft and driveshaft are disconnected from the engine. The motor may now drive the compressor by deriving power from the battery.
It would be desirable to provide a control method for controlling hybrid compressors that would minimize motor stall torque and allow for a gradual ramping up of the speed of the electric motor. The control method should eliminate a large in rush current during motor start up as well as optimize motor speed and efficiency.